Hybrid circuit arrangement



Oct. 20, 1959 A. WALTER 2,909,733

HYBRID CIRCUIT ARRANGEMENT Filed oct. 29, 195e f /7 34 3/ /M y,

2 3, l /9 341 32 lak?, [2,42 21 Z w52 4 z 4 /j 42" INVENTOR. Maf /w/f BY impedance.

of transmission apparatus.

,three vof .the Ypairs .of terminalsrof the fhybrid United States Patent 2,909,733 l lRataltred :20,413.59

HYBRID 'CIRCUIT ARRANGEMENT Arthur Walter-, Konstanz/-Boden'sea Germany, ass'gnor4 to Konstanz am Bo- The ,present invention relates `toa hybrid .circuit arrangement. More particularly, the lpresent invention yrelates to a hybrid -circuit arrangement fhaving three pairs of terminals, each of which has the same characteristic Hybrid circuit Varrangements are used in varioustypes are used in telephone repeater circuits wherein it is necessary .to .use one pieceof apparatusfsuch as anzamplifier,

.ina transmission line which.carriestelephonef coniversatial 'transformer is used having three windings. The terminals ofthe hybrid vcircuit are v`connected to respec- Forexample, hybrid circuits tively different windings of the diiferential transformer. 'l

With suchconventional hybrid circuit arrangements, it 'is necessary to use an'additional transformer between the differential transformer and one lof the pairs of output terminalsto provide proper .matching mpedances :for all v circuit :arrangement. A. .Itis clear that the use of `such an additional transformer for `impedance matching purposes :increasesthe .physical size of -the hybrid circuit apparatus` by a -great amountand also increases lthe lcost of fabrication of such a circuit. Q s

The presentinvention provides -ahybrid circuit arrangement having three pairs of terminals, :the characteristic impedance `betweeneach of thepairs of `terminals Vbeing equal. This is accomplished Without the use Aof any additional transformer.

Accordingly, it is an object of the present ,invention to overcome `the disadvantages of the vconventional arrangements described hereinabove.

A second objectof the present invention `is to provide a new and limproved hybrid circuit arrangement.

Another object of the present invention is to provide a new and improved hybrid circuit arrangement havingat least rthree pairs of terminals, ,the characteristic -im pedance-.between each pair of theterminalgs fbeing equal and wherein the hybrid circuit `arrangement usesonly one transformer.

Afurther object of thejpresentfinvention is togprovide a hybrid circuit arrangement 'using ari-impedance network to provide characteristic impedances betweenfeach' of the pairs of terminals` of a hybrid circuit arrangement.

Still another object of the present invention is to provide a hybrid circuit arrangement wherein an asymmetrical quadripole is used for properly equalizing the characteristic impedances of-each of the terminals of the hybrid 'Y'.

circuit arrangement. l

With the above objects in Iview the present invention mainly consists of a hybrid circuit arrangement having .three pairs of terminals and including a transformer hav- -ing Iat least one primary 'winding vand one secondary winding, the Aends of the Asecondary winding being v.connected Irespectively :to .one of the pairs of .terminals Aand Ybeing.' ternfijinated bya characteristic vimpedance Z, lthe primary 'winding :having -a center tap, a twoterminal bal- -,ar 1 cing network having one :terminalI thereof connected lto yone end ofthe:primary-windingandhaving ani impedance ZZ, the .Second pair .of the hybrid terminals ybeing vconnectedrespectively Fto 4theiother itermin'al -of;the.balancing rnetworkgandthe y`.center-,tap .of the primary winning, :the transformation rati'o"between ysaid' primary Iand secondary -willdfngsbeing' selected Vin such azmanners'that'a matching impedance ZZ is thereby'determined between rsaid 'other terminal of said balancing network andthe ,other ken'dbf `said primary'winding, aswelly as across said' vbalancing network, .and :an f asymmetricalquadripole having-an input image impedancecqual' to Zihaving Yan' output `2iinpedance equal to ZZ, 4-thefo'utput of the.quadripole@being-connected between lthe other terminal of the balancing network and the fother .zend of vthe primary lwinding, the. inputeof'jthe lfquadripole Ybeingconnected =tonthe` third pair of 'terminals of thephyhrid circuit whereby each of thelpairs of tei'- lminalsoffthef hybrid circuit' arrangement ihas an *impedan'ce equal'to Z. s' iIn .stillanother'embodiment of the -presentjinventiqn the transformer has an additional centerftapped primary winding so that the entire hybrid circuit is completely 'balanced with respecttofground. Y The novel-'features-which are considered as character- -isticfvfor the -invention arefset forth in particular in the appended claimsyThe linvention itself, ihowever, `both `as to 'its ;cor 1`st1'uctionl and its methodof operation, to- -getherwith additional objects andadvantage thereof,'will be best understood from the"` following `c lesc'ription. of specific embodiments when read in connectionvywith the Qcnnected respectively .to the ends` of Ethe', Secondary winding .14.bY means .otppnductorsl and 17 a'reafrst pair 6ftenninals 1 8. and Y19- ofthe `hybird circuit,ar.ra1.1f.; ment. vThe .transformation ratio ,of transformer :110' is suchV that the characteristic ,impedance appearing across the Scndary Winding 14,gbetween ,the irlsf pair of Lte'rminals 18 and 19, equals the value Z, aswill'be explained below.

' Connected to one end 12" of the primary winding 12 by means of a conductor 21 is one terminal of a twotermnal balancing networkZZ. The other terminal Z3' fof the network 22 connected-by conductor Z3 to a junction point 24. The'fsecond pair of terminals 26 and 27 of thehybridficircuit arrangement-are respectively connectedtothe center tap 13 ,hyconductQr 281andjtothe iunetionnointlby means-.0f conductor' 29.` l..

Connected t0' one .eln'dcf theprimarv winding the diiferentialtransformer :10 Visthe .junction peinti ,4f New'withenveufmal .hybdrireuitslvin tast' .to the hybrid'circnit accordingto the 'invention, Junction points 31 and 24 respectivelypwould be directlyv connected 'to the third; pair 'Qf terminals Qt thehybrid circuitarrar'lgement and be matched lby, an impedance which equals the valueijthetran'sformation ratiobetween secondary and primary windings being therefore chosen to establish the same impedance between terminals 18 and 19 as between junction points 31 and 24. Accordingly with such known hybrid circuits the two-terminal balancing network 22 mentioned above would also have to have an impedance equal to Z, the primary of the differential transformer being thus balanced with regard to the secondary winding and to the first pair of terminals connected thereto. As is well known, in this balanced state, no transmission nor any impedance transformation is possible from the rst pair of terminals 18, 19 to any element connected between center tap 13 and junction point 24 and vice-versa, as intended. Therefore, between center tap 13 and junction point 24 appears an impedance which equals half the value of the impedance existing across junction points 31 and 24. In the conventional hybrid circuit, this means that an impedance of Z/ Z appears between center tap 13 and junction point Z4, necessitating the use of an additional transformer in order to provide for the second pairs of terminals the same value of characteristic impedance as is effective across junction points 31 and 24, that is the value Z.

Contrary to this conventional arrangement, with the hybrid circuit according to the invention the doctrine has been abandoned that the proper matching impedance between junction points 31 and 24 has to be equal to the characteristic impedance appearing between the first pair of terminals 18 and 19 and the second pair of terminals Z6 and 27, respectively.

In the hybrid circuit arrangement according to Fig. 1, as stated above, the transformation ratio of transformer 1@ is chosen so that the characteristic impedance appearing across its secondary winding 14, i.e. between the rst pair of terminals 18 and 19, has only half the value of the matching impedance required between junction points 31 and 24. The latter as well as the impedance of the two-terminal balancing network 22 equals the value ZZ, whereby the value of Z is obtained for the impedance between the first pairs of terminals 1S and 19.

The value of the impedance appearing between center tap 13 and junction point Z4, which equals half the value of the impedance effective between junction points 31 and 24, will now be equal to Z, which is the intended characteristic impedance for the second pair of terminals 26 and 27.

Also connected to the junction points 24 and 31 is the output of an asymmetrical quadripole made up of the resistors 32 and 33 and having terminals at 31, 24, 34', 36. The third pair of terminals 34 and 36 of the hybrid circuit arrangement are connected to the opposite ends 34', 36' respectively, of the resistor 33 representing the input of the quadripole.

The values of the elements of the quadripole are arranged so that the input image impedance between the terminals 34 and 36 equals Z and the input image impedance across the output junction points 24 and 31 of the quadripole matches the characteristic impedance ZZ existing across the points 24 and 31. These values can be established from the following relationships:

wherein 232 and Z3?, are the impedance values of the elements 32, 33, respectively.

Accordingly, the above-described arrangement of Fig. l provides a hybrid circuit arrangement having three pairs of terminals 18, 19; 26, Z7; and 34, 36. The characteristic impedance across each of these pairs of terminals has the value Z. The quadripole has the output image impedance value ZZ which matches the characteristic impedance ZZ across the junction points Z4 and 31.

This arrangement permits the transfer from a twowire transmission system to a four-wire transmission system and vice versa. In addition, the equal characteristic impedance Z is obtained at each of the pairs of output terminals even though the impedance appearing across the secondary winding 14 of the differential transformer 10 is equal to one half of the matching impedance across the junction points 24 and 31. This is a further distinction between the hybrid circuit arrangement of the present invention and conventional circuit arrangements wherein the impedance at the terminals of the secondary winding is equal to the impedance at the terminals of the primary winding which, by comparison, correspond to the above mentioned junction points 24, 31.

The arrangement of Fig. l provides an additional advantage in that the complex impedance of the transmission line looking into the terminals 34 and 36 is made more uniform due to the use of the quadripole. This facilitates balancing of the line. In addition, in a balancing network 22 made solely from one or more resistors and capacitors respectively, any capacitors that are used can be smaller than in the conventional hybrid circuit arrangements.

Referring now to Fig. Z a second embodiment of the present invention will be described. The parts of Fig. Z which have the same function as the parts of Fig. l have the same reference numerals. In this embodiment in place of the balancing network 22, a balancing network is provided which comprises a balancing network having an impedance equal to Z. The impedance of the balancing network 41 accordingly corresponds to the usual value for balancing networks in conventional hybrid circuit arrangements. To properly match the impedances in this arrangement, a second quadripole having terminals at 42.', 43', 12", Z3' and made up of the resistors 4Z and 43 is connected at 12" with the primary winding 12 of the diiferential transformer 10 and at 4Z' and 43 with the impedance 41, said second quadripole corresponding to the quadripole 32, 33. In this manner, if conventional balancing networks as shown at 41 are more easily commercially available, it would be possible to use the same with the improved circuit of the present invention.

In addition to the above advantages, the use of the second quadripole having an input impedance equal to Z and an output impedance equal to ZZ permits a more proper balancing of the hybrid circuit arrangement. Therefore, a higher precision can be attained thereby improving the transmission coeicients between the terminal pairs 13, 19 and 26, 27.

Referring now to Fig. 3, still another embodiment of the present invention is illustrated. This arrangement provides a balanced arrangement of the differential transformer and the quadripole with respect to ground. In the embodiment of Fig. 3, the differential transformer 10 has a secondary winding 14', a pair of primary windings 11, 12.' with a center tap 54 and another pair of primary windings 51 and 52 with a center tap 53 therebetween. The pair of terminals Z6 and 27 are connected between this center tap 53 and the center tap 54 of the windings 12' and 11', respectively.

In this embodiment the quadripole with terminals 31, 24', 36', 34' still has an input image impedance equal to Z and `an output image impedance equal to ZZ. However, the quadripole comprises not only resistors 32, 33, but an additional resistor 56. The impedances of the quadripole are obtained from the following equations:

(Zas) (Z) wherein 232, 233, 256 are Vthe .impedance valuesfo'f -the elements 32, 33, 56 respectively.

'Thesecondquadripole forming part of the balancing network `and having the four terminals at 12, 23', 43', 42' is also composed mainly of three elements 42, 4 43 corresponding to the quadripole comprising the resistors 32, 33, 56, and connected at 42', 43 with an impedance 41 similar to the arrangement of Fig. Z.

In the arrangement illustrated in Fig. 3, the proper characteristic nimpedance is obtained at each of the Vthree pairs of terminals'of -the hybrid Lcircuit arrangement. However, the arrangement is completely balanced with respect to ground so that undesirable ground currents between different grounded parts of the circuit can be eliminated if these are large enough to be undesirable.

A further advantage of the present invention is that the quadripole inserted to provide the proper impedance matching for the hybrid circuit introduces attenuation which is usually required in the transmission line to keep the level of the transmitted signals within prescribed limits. This usually has to be provided by means of attenuation pads in each of the lines of the transmission circuit. Therefore, the use of the quadripole eliminates, if desired, the necessity for any additional attenuating elements.

It is therefore apparent that with the described circuit incorporating the principles of the present invention, a hybrid circuit arrangement is obtained having three pairs of terminals, the characteristic impedances between each of them being equal. This characteristic impedance is achieved without the necessity of having more than one transformer in the circuit.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of circuit arrangements dilering from the types described above.

While the invention has been illustrated and described as embodied in hybrid circuit arrangements using an asymmetrical quadripole, it is not intended to be limited to the details shown, since various modications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others' can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A hybrid circuit arrangement having three pairs of terminals, comprising, in combination, a differential transformer having at least one center-tapped primary winding and a secondary winding, the ends of said secondary winding being connected respectively to one of said pairs of terminals, said secondary winding being terminated by a characteristic impedance Z; a two-terminal balancing network having one terminal thereof connected to one end of said primary winding and having an impedance ZZ, the second pair of said hybrid circuit terminals being connected respectively to the other terminal of said balancing network and said center tap of said primary winding, the transformation ratio between said primary and secondary windings being selected in such ya manner that a matching impedance ZZ is thereby determined between said other terminal of said balancing network and the other end of said primary winding, as well as -across said balancing network; and an asymmetrical quadripole having an input image impedance equal to Z `and an output image impedance equal to ZZ, the output terminals of said quadripole being connected between said other terminal of said balancing network 6 and said other endvof saidprimary winding, the input terminalsof said quadripole being connected -to the -third pair of terminals of saidhybrid circuit whereby each of said pairs of terminals of said hybrid circuit arrangement 'has an impedance equal to Z.

Z. A hybrid circuit arrangement balanced with respectto ground and having three pairs of terminals comprising, in combination, a differential transformer having two center-tapped primary windings and one secondary winding which is terminated 'by a characteristic impedance Z, the ends of said secondary winding being connected respectively to one of said pairs of terminals; a two-terminal balancing network having an impedance ZZ, one terminal thereof being connected to one end of the rst of said primary windings and the other terminal thereof connected to one end of the second of said primary windings, the second pair of said hybrid circuit terminals being connected respectively to the center taps of said first and second primary windings, the transformation ratio between both said primary windings and said secondary windings being selected in such a manner that ya matching impedance ZZ is thereby determined between the said other. ends of said first and second primary windings, as well as across said balancing network; and an `asymmetrical quadripole having an input image impedance equal to Z and an output image impedance equal to ZZ, the output terminals of said quadripole being connected between said other ends of said first and second primary windings, the input terminals of said quadripole being connected to the third pair of terminals of said hybrid circuit whereby each of said pairs of terminals of said hybrid circuit arrangement has an impedance equal to Z.

3. Apparatus as claimed in claim l wherein said quadripole includes two impedances having the values `Zag and Zas, respectively, said impedance values satisfying the following two equations:

quadripole includes three impedances having the values Zgz, Z33 and 256, respectively, said impedance values satisfying the following three equations:

(Zas) (Z) (Zes-FZ) 5. An arrangement as claimed in claim l, wherein said two-terminal balancing network having an impedance ZZ comprises a two-terminal balancing network having an impedance Z and a second asymmetrical quadripole the input image impedance of which is equal to Z and the output image impedance of which is equal to ZZ, the input terminals of said second quadripole being connected to the terminals of said balancing network having an impedance Z, the output terminals of said quadripole forming the two terminals of said two-terminal balancing network having an impedance ZZ.

6. An arrangement as claimed in claim 5, wherein said asymmetrical quadripoles are substantially composed of resistors.

7. An arrangement as claimed in claim l, wherein said asymmetrical quadripole is substantially composed of resistors only.

8. An arrangement as claimed in claim 2, wherein said two-terminal balancing network having an impedance 2Z comprises a two-terminal balancing network having an impedance Z and a second asymmetrical quadripole the input image impedance of which is equal to Z and the output image impedance of which is equal to 2Z, the input terminals of said second quadripole being connected to the terminals of said balancing network having an impedance Z, the output terminals of said quadripole forming the two terminals of said two-terminal balancing network having an impedance 2Z.

9. An arrangement as claimed in claim 8, wherein said asymmetrical quadripoles are substantially composed of resistors.

l0. An arrangement as claimed in claim 2, wherein said asymmetrical quadripole is substantially composed of resistors only.

References Cited in the le of this patent FOREIGN PATENTS 

